Field of the Invention
The present invention is broadly concerned with overall auger assemblies and methods useful for the creation of bores at sites where solid earth has a layer of loose overburden, so as to quickly and inexpensively form such bores, especially during the fabrication of cast-in-place pilings. More particularly, the invention concerns such auger assemblies, as well as specialized auger bit assemblies forming a part of the overall augers, wherein apparatus is provided adjacent the working end of the auger or bit assembly which is operable to compress the loose overburden material in order to form a self-sustaining, compressed peripheral annulus of the material. Such apparatus preferably includes an arcuate rake above the working end of the auger or bit assembly.
Description of the Prior Art
One favored method of forming structural piles is through the use of auger pressure grouting techniques. During such operations, an upright metallic support frame is positioned adjacent a pile site and is supported by means of a mobile crane. An auger assembly is associated with the support frame, and includes an elongated, flighted auger having a hollow central shaft, as well as an upper auger motor. A supply of fluid grout is also provided, typically by means of a mobile grout truck, with the grout supply being connected to the auger shaft through a flexible hose. During pile-forming operations, the auger is first shifted downwardly during rotation thereof, so as to screw the auger into the earth. When the auger has reached a desired depth, the auger is withdrawn in order to remove the spoil. Simultaneously, fluid grout is directed under pressure through the auger shaft so as to create the pile.
While this technique is extremely advantageous when creating piles in virgin soil, problems may arise if the overburden in question is loose or of low density. For example, in certain areas of the country landfill sites have been largely exhausted, and is now desired to create waste disposal plants on those sites. Unfortunately, many such landfill sites have a low density overburden consisting of previously deposited municipal solid wastes. In such cases attempts at using the straightforward pile-forming technique described above may lead to excessive consumption of grout, in that as the grout is fed under pressure through the auger shaft, it spreads laterally outwardly through the overburden rather than creating a unified, upright pile.
One response to these difficulties is to employ an upright, tubular metallic casing to confine the grout. This expedient is generally known in the art, and methods have evolved for efficiently placing such casings in the earth. However, it has been discovered that use of casings is not a complete answer to the problem of forming piles in landfill sites, because the piles tend to uproot or turn during the pile-forming operations when the auger moves upwardly and downwardly therein. This problem is particularly acute when use is made of lower cost corrugated metallic, as opposed to the more expensive, heavy metallic straight tubes.
U.S. Pat. No. 4,966,498 describes another technique for dealing with the problem of loose overburden bore sites. The '498 patent describes use of a tubular collar inserted into the loose overburden, with a specialized gripping structure to hold the collar in place. While these techniques are quite useful, they can be relatively expensive owing to the need to use the specialized collar and gripper structure.
General design considerations for auger assemblies used in the fabrication of cast-in-place pilings are described at https://www.fhwa.dot.gov/engineering/geotech/pubs/gec8/gec8.pdf.